Hydraulic system for damping or retarding moving bodies



Dec. 1, 1942. c. R. HANNA 3 5 HYDRAULIC SYSTEM FOR DAMPING OR RETARDING MOVING BODIES Filed Aug. 25, 1958 4 Sheets-Sheet l INVENTOR v ITNESSES: w 4 I Cliniofl RHanna- W 5' E ia 79W ATTORN EY 'Dec. 1, 1942. c. R. HANNA HYDRAULIC SYSTEM FOR DAMPING OR RETARDING MOVING BODIES Filed Aug. 25, 1938 4 Sheets-Sheet 3 J i? INVENTOR UQT jITNESSES:

ATTORNEY Dec. 1, 1942; c. R. HANNA 2,3 3,

HYDRAULIC SYSTEM FOR DAMPING 0R RETARDING MOVING BODIES Filed Aug. 25, 1958 4 sheets sheei 4 lNVENTOR BY 7 ATTORNEY Patented Dec. 1, 1942 HYDRAULIC SYSTEM FOR DAMPING OR RETARDING MOVING BODIES Clinton a. Hanna, Wilkinsburg', Padasslgnor to Westinghouse Electric & Manufacturing Company; East Pittsburgh, Pa a corporation of Pennsylvania Application August 25, weasel-n1 No. 226,763

8Claims.

My invention relates to a hydraulic control system for damping, or retarding the movement of a movable body and particularly a movable body mounted to oscillate, or to move on both sides of a central or neutral zone.

One object of my invention is to provide a An object of my invention is to provide a twoway hydraulic control system for damping the movement of a movable member that is mounted for oscillation on two sides of a neutral zone.

neutral or center zone, hydraulic control systems have many advantages because a relatively noncompressible fluid such as oil may be used as the control medium, while at the same time serving as a lubricant for the moving mechanism. With the use of oil as a control medium, simplevaive structuresmay be employed of relatively small size to control relatively heavy masses.

In the present case, I have shown a particular application of my hydraulic control system to damp the precession movement 01' a gyroscope. In order that a gyroscope may be used as a stabilizing device, for example, on a ship or other A further object of my invention is to provide v the precession of a gyroscope.

A further object of my invention is to provide a hydraulic control system to damp the precession of a gyroscope, and to automatically center the gyroscope according to the total swing or excursion of the gyroscope.

Another object of my invention is to provide a hydraulic control system, for a. gyroscope, in which the damping effect shall be maintained independent of the viscosity of the fluid used in'the hydraulic system.

A'further object of my invention is to provide a hydraulic control system that shall damp the precession of a gyroscope, and that shall, at the same time efiiect an automatic centering of the gyroscope at an artificial zone, depending upon the progressively varying average excursion or swing of the gyroscope in its precession movements.

Still another object of my invention is to provide a control system, for a gyroscope, that shall damp the precession velocities to keep them below a fixed maximum speed.

Another object of my invention is to provide a hydraulic control system for general applications of retardation, in which a pressure shall be developed proportional to the volumetric velocity of the hydraulic fluid, or medium, by means of a simple and easily constructed valve system.

In controlling the movement of heavy masses that are so mounted as to oscillate, or to swing from one extreme to another across a variable vehicle or carriage susceptible to rolling motion, the precession movements of the gyroscope should be retarded or braked to provide a reaction pressure by means or which the gyroscope could introduce a stabilizing force to maintain the normal position of the moving body upon which it is mounted.

In order to provide a satisfactory hydraulic system of control for the gyroscope, the system should be able to maintain its impedance characteristics against the precession movements independently of the viscosity of the -fluid' or medium used in the hydraulic circuit. Such a system to be satisfactory should also provide an.

automatic centering arrangement for the gyroscope, to establish an artificial center when the excursions or .precessional movements of the..

cession should be greater than half of the ship'sroll period, but the precession should be limited to prevent overrolling beyond a sixty degree angle.

In applying the hydraulic control system of my invention to the damping of the precession movements of a gyroscope, I preferably mount the control valve device on the bearing shaft of the frame or gimbal for the gyroscope wheel in such manner that the precession movement of the gyroscope will'tum a vane or blade within a fixed stationary housing to force the hydraulic medium, such as oil, into a retarding circuit controlled by the device. The valve structure of the device is so arranged as to be cumulatively aflected, and to change the area of the valve passage opening with each precessional movement of the gyroscope in one direction. As the gyroscope precesses in the opposite direction, the valve structure is cumulatively restored to change its opening area back to the original or initial quantity. Thus, so long as the precessional movements are substantially equal in their angular displacements, the valve structure will be continually shifted to a position on one side of its neutral position, and then shifted to the other side of its neutral position. In this manner, the position of the control valve assembly will be governed by the progressive differential of the aggregate precessional movements. So long as such precessional movements are equal and opposite, the control valve assembly will remain substantially balanced in its effect. If the precessional movements tend to preponderate, however, in one direction, the valve assembly will be cumulatively affected to establish a new artificial neutral or central zone, within the extremities of the precessional movements under those conditions. When the precessional movements subsequently preponderate in the other direction, as the moving body tends to resume its normal central position, the position of the valve structure is correspondingly modified to shift the artificial neutral back to the actual neutral or central zone.

While the valve structure shifts position to establish an artificial neutral or central zone, it also modifies the damping effect, upon the precessional movements, to increase the damping or retardation effect upon the precessional movements in that direction in which the precessional movements, for the time being, preponderate. In that manner, the control system automatically compensates to increase the retarding effeet against further movement of the controlled body in the direction in which its unbalancing motion tends to preponderate.

By employing the valve structures of proper designs and arrangements, the viscosity of the oil may be eliminated as a control factor, so that the operation of the damping system will be independent of oil viscosity. In this system, the valve structures are designed and cooperatively arranged to provide a pressure that is proportional to the volume velocity. Specifically, such pressure is obtained by a spring valve, whose opening area is proportional to pressure, and a thin-walled orifice. A separate spring-controlled valve that is responsive to the oil pressure serves to limit the volume velocity of oil displacement and thereby limits the maximum value of precession.

The construction of a hydraulic control system, as applied to control the precession of a gyroscope, and the manner in which such system is applied to the gyroscope, in accordance with the principles of my invention, are illustrated in the accompanying drawings, in which:

Figure 1 is a schematic view of a gyroscope structure illustrating a mounting of the hydraulic damper for controlling the precession movements;

Fig. 2 is a vertical and longitudinal sectional view of the hydraulic damper structure;

Fig. 3 is a transverse sectional view, of reduced dimension, taken through the vane and pressure chamber of the assembly shown in Fig. 2;

Fig. 4 is an end elevational view taken from the front or left-hand end of the assembly shown in Fig. 2;

Fig. 5 is a plan view of the assembled un t shown in Fig. 4 with portions broken away to illustrate the valve control structure and the passages to the control valve from the pressure compartments;

Fig. 6 is an enlarged longitudinal sectional view of the valve assembly of the arrangement shown in Fig. 2;

Fig. 7 is an enlarged plan view, partly in section, of the valve control assembly of the arrangement shown in Fig. 5;

Figs. 8 and 9 are front elevational views of the one-way clutches that operate the center valve stem, and Fig. 10 is a graph of the operating curves of the valve units.

As shown in the drawings, a gyroscope I0 is mounted upon a movable body II that is to be controlled to maintain a condition of stability. For the purpose of this description, the body I I will be considered to be a ship.

The gyroscope I0 comprises the usual gyroscope wheel I2 mounted for rotation around a vertical axis between two bearings I3 and II in a ring or housing I5. The'housing I5 is mounted for rotation about a horizontal axis on trunnions extending into the two bearings I6 and IT. A shaft I8, that is rigidly connected with the housing I5, extends through the bearing I1 and serves to support and to operate a hydraulic control device 20, to control the precession movements of the gyroscope wheel I2 about the axis of the trunnions.

The control device 20 embodies a vane 2| that 'is splined on the shaft I8. The vane 2| is disposed within a housing 22 in such manner as to divide the space within the housing into two compartments or compression chambers 23 and 24, that are completely filled with a relatively non-compressible hydraulic medium, such as oil. The housing 22 is anchored at its base by a suitable device 25, to prevent rotation of the housing when the vane is moved by precession movements. The shaft I8 is connected to the supporting housing I5 in which the gyroscope wheel is mounted. The precessional movements of the gyroscope wheel l2 will, therefore, turn the frame I5 in its bearings I6 and I1, and will -correspondingly turn the shaft I8 within the stationary housing 22. The power vane 2| will, thereupon be rotated and will exert pressure upon the oil in the compartment towards which the power vane 2I is moved by the precession of the gyroscope. The oil will then be forced out of that compartment by that pressure of the vane 2|. By establishing a suitable resistance to the movement of that oil, a reaction pressure can be established to damp the movement of the vane 2 I, and thereby to dampen the precessional movement of the gyroscope; That reaction pressure then acts to stabilize the body I I.

If chamber 23 is the pressure compartment, oil is forced out of it by the moving vane 2|, shown in Fig. 3, and is forced into the valvecontrolled passages shown more clearly in Figs. 2, 5, 6 and 7. From the pressure compartment 23, the oil is forced into a communicating passage 30 containing a spring-biased pressurecontrolled cut-oil? valve 3|. Pressure compartment 24 communicates with a passage 23 containing a similar valve 3 I The passage 30 (see Fig. 7) extends into the body of the valve housing block 32 mounted above the pressure chambers. The inner end of the passage 30 is provided with a smaller diameter than the outer end of the passage, the latter end being slightly enlarged to provide a tapered shoulder or seat 33 for the valve 3|. The outer end of the passage 30 is threaded and is arranged to be closed by a similarly threaded plug 34. The inner end of the plug 34 is slightly reduced in diameter and is provided with a cen-' tral positioning boss 35 to locate and seat a pressure biasing spring 33 for the valve 3|. The spring 35 is initially unstressed so that the area of the valve opening will be proportional to pressure.

The valve 3| is of the sleeve type and consists of a hollow cylindrical member with a shank section 31 of an external diameter to provide a sliding fit with the inner portion of the passage 3| is slightly enlarged and is provided with an outwardly diverging inclined or tapered surface 45 of the same inclination 'as the seating surface 33 of the shoulder in the passage 33 so that the valve may provide a good flt. The head end of the valve 3| is provided with a central seating boss 42 of a shape and diameter corresponding to the seating boss 35 onthe closin plug 34, and cooperates with that seating boss 35 to maintain the pressure spring 33 properly seated in operative position between the plug and the valve. A small by-pass leak orifice 3|a is provided in valve 3|, at the front of its central passage, for a purpose to be referred to later. The cut-out slot 33 in the valve cylinder, and the end wall 33 of the cut-out slot are so positioned that the end wall 33 will be disposed within the passage 33 and below the transverse plane of the smallest diameter of the tapered seat 33 against which the valve 3| rests in its closed position when the valv 3| is fully closed.

When the oil pressure overcomes the pressure of the valve closing spring 33, the spring 33 is compressed by the movement of the valve 3| and the slot 331s moved to a position at which the oil may move the transfer passage 4| to a centering control valve generally indicated at 45. The centering valve 45 is illustrated in Fig. and somewhat more in detail in Fig. 7. It comprises mainly a central valve sleeve or inner cylinder 43 and an encircling sleeve or outer cylinder 41. The outer sleeve 41 is provided with a group of openings 5| angularly disposed around the circumference and extending through the wall of the cylinder 41 at a zone where the openings 5| will communicate with the transfer passage 4| when the outer cylinder 41 is in its operating position.

The outer cylinder 41 is also provided with a similar group of angularly spaced openings 52 around its periphery andextending through its wall in a region axially'displaced from the openings 5|, so that the openings 52 may communicate with a second transfer passage 53, that is associated with the other pressure compartment 24, through passage 23, which will be referred to later.- The space or distance between the openings 5| and 52 is, of course, closed by the wall section 53 in the outer cylinder 41 of the centering valve. That wall section 53 is specifically referred to since the axial dimension along that wall represents a control dimension in the operation and function of the centering valve 45.

, Beyond the openings 52 the outer cylinder 41 embodies a portion 54 having a smaller internal diameter, and it is internally threaded toreceive a correspondingly threaded end portion 55 of the inner control sleeve valve 43. Beyond the threaded portion the outer sleeve 41 embodies an extension 55 that serves as a guide and seat and also as a stop element for a pressure responsive valve 51 that will be referred to and described in detail later. 1

Returning again to the outer sleeve 41 of the centering valve, it will b observed, as shown in Figs. 6 and '1, that the front portion of the outer sleeve 41 is provided with an enlarged section 53 externally threaded to fit into a threaded section 53 in the valve housing block 32. The

outer end of the outer sleeve 41 is providedwith an annular flange 55 which seats against an oil seal lock washer 3|. The outer sleeve 41 is also provided with a series of openings '32 in,

the shank or body of the sleeve 41, where the openings will communicate with the space 53 between the enlarged threaded section 53' and the valve block, in order to prevent high pressure at the gaskets and packing and also to provide access for lubrication for the inner valve sleeve 43 where it engages the inner wall of the outer valve sleeve 41. The end of the outer sleeve '41 is also provided with an internal thread 34 of slightly larger diameter than the internal \sleeve 43, in order to receive an oil seal washer 35 and a locking and positioning plug 33 for the oil retaining washer 35.

As shown in Fig. 6, the inner end of the internal sleeve 43 is hollow to provide a tubular section, and the outer end is solid. The inner end is provided with one pair of peripheral slots 1| of substantially rectangular shape 'with the center lines of the slots 1| in alignment with and in the plane of the inner or rear end edges of the openings5| of the outer cylinder 41. A similar plane of the forward edge surfaces of the'openings 52 in the outer sleeve 41. The relationship between the openings 5| and 1|, and between the openings 52 and 12, is such that when the internal sleeve 43 is in its normal neutral position, the openings 1| and 12 will provide passages of correspondingly equal areas to the transfer passages 4| and 53, to permit oil to be transferred from the transfer passages into the central opening of the cylinder section of the internal sleeve 43.

When the sleeve 43 is axially shifted, however, the effective openings of the slots 1| and 12 with respect to their associated transfer passages 4| and 53 will be changed. As the effective area of the opening H is increased; the effective area of the opening 12 will be decreased, and vice versa.

By means of such arrangement, the internal valve sleeve 43 cooperates with the external sleeve 41 to provide a balancing or centering function in controlling the passage of oil from the two pressure compartments 23 and 24 into the internal valve sleeve 43.

terfial sleeve 46 may be actuated to shift the openings H and 12 relative to the openings i and 62. i

If, the ibody upon which the gyroscope is mounted is subjected to a series of external forces that preponderate in one direction for an interval of time, the gyroscope will be caused to precess correspondingly to a preponderately greater extent in one direction. As a result, the precessing movements of the gyroscope will not by symmetrical with respect to the normal or actual central or neutral axis. In order that the precessing movements of the gyroscope may be made symmetrical and equi-angular with respect to the neutral axis, it becomes necessary to shift such neutral axis and to establish it as an arbitrary or artificial axis, where, and about which, the precessing movements of the gyroscope will be equally and symmetrically distributed.

It is also desirable, in addition to artificially centering the neutral axis of the gyroscope during its precessional movements, to provide a compensating factor for the preponderating external force that is unbalancing the supporting member for the gyroscope and causing the gyroscope to precess. That is, the resistance to the external force, as measured by the precession, should be greater where that force tends to cause pre- 'ponderant precession. I utilize the centerin valve for that purpose by restricting the effective szes of the valve openings or slots H or I2 in internal sleeve 46, to such an extent as may be necessary, in order to provide greater impedance to the precessional movement of the gyroscope in the preponderating direction with respect to its actual normal axis of rotation. In that manner the gyroscope tends to establish a greater restoring force in opposition to the preponderant unbalancing forces that are impressed upon the device to which the gyroscope is applied. Conversely, the other slot of the valve sleeve, that is, either 12 or, as the case may be, is correspondingly shifted to provide an effective enlargement of the effective opening between the corresponding transfer passage and the inside passage of the internal valve stem 46, to reduce the impedance to precession movement in the restoring direction towards true balance. be understood that impedance is increased for the direction having excess motion and vice versa.

To control the movement oi the inner valve sleeve 46 in either direction, two uni-directional clutch devices 14 and 16 are employed. The one-way clutch 14 operates to rotate the inner valve stem or sleeve 46 counter-clockwise as viewed in Figs. 4 and 8, and the other one-way clutch operates to rotate the inner stem or sleeve 46 in a clockwise direction, as shown in Figs. 4 and 9.

The operation of the respective uni-directional clutches l4 and I5 is controlled according to the direction and extent of movement of the power vane 2|. The shaft l8 which supports the power vane 2i also supports an end plate 16 upon which are mounted two actuating pins 11 and 18, located to be equi-distantly disposed from a normal vertical center line passing through the center of the shaft l6 and the center of the valve sleeve 46. As shown in the side view in Figs. 2 and 6, the actuating pin ll extends outwardly further than the pin 11, and upwardly as an L-shaped element to reach its clutch device, which is axially displaced on the external extension or actuating section 13 of the internal sleeve 46.

It will The uni-directional clutch 14 comprises, brief- 1y. an annular ring or actuator provided ,with

two integral depending operating arms 8i and 82 as a fork, a clutch roller 83, a back arm 84 on the actuator, and an overcenter spring 85, that is pivotally connected at one end to the back arm 84 of the actuator, and that is pivotally anchored at its other end to a stationary pin 88. A stationary stop 81 limits the motion of the clutch actuator 80 and, therefore, of the clutch, in one direction, anda stationary stop 88 similarly limits the motion of the clutch in the opposite direction. Spring 88 biasses the clutch roller 88 to engaging position between the actuator of the clutch I4 and the actuating extended portion 13 of the internal sleeve 46, to prevent any lost motion in the actuating operation.

Theclutch 15 is provided with similar elements designated by the same numerals primed, except that it is mounted with the roller 83' disposed to engage a surface that is oppositely inclined to the surface 90', so that it will disengage when the clutch 14 engages and will engage when the clutch l4 disengages. I

The purpose 'of the overcenter springs and 85' on each clutch is to compel each clutch to move to its extreme-position in either direction of actuation, in order that the fork arm such as 8| or 82, by means of which the clutch has been actuated to one position or the other, shall be moved out of the way of the actuating pin 11 or 18 of the clutch, upon the return movement of that pin. when the power vane 2i returns to its neutral position in response to the return of the gyroscope towards its neutral position.

So long as the precessional movements of the gyroscope are equal from its normal neutral center line, each clutch motion that causes a corresponding movement or turn of the central sleeve 46 will be counter-balanced and counteracted by a corresponding movement eifected by the other clutch, to restore the sleeve to its initial position. Consequently, so long as the precessional movements of the gyroscope are symmetrical, the valve movements will be symmetrical and will establish or maintain an average zero movement with respect to the normal neutral position of the centering valve 46.

When the external motion-controllingforces preponderate in one direction against the member or device upon which the gyroscope is supported or mounted, the gyroscope will correspondingly precess to a greater degree angularly in one direction than in the other. As the low side swing becomes less, it will tend to reach a value at which there would be no restoral of the internal sleeve valve 48. Consequently, the con-- tinued precessional movements in the preponderating direction' of movement with respect to the normal center will cause continued actuation of the internal sleeve valve 46, by such movements in the preponderating direction, without any corresponding restoration or return movements of the internal valve sleeve 46. As a result, the internal sleeve 48 will be shifted to a position that will represent and temporarily establish a new artificial center line or neutral zone about which the angular movements of the power vane 2| will be equal. Thus the precessional movements of the gyroscope will be artificially equalized with respect to the temporary artificial neutral zone or center line for the gyroscope.

While the internal valve sleeve 46 is in such off-normal position, in accordance with the new artificial center line. the valve openings Ii and "i2 will be shifted with respect to their normal center-line positions, and one of the openings, either II or 12 depending upon the direction of the preponderance, will be shifted to introduce a constricting effect by reason of the reduced dimension in the area of the opening presented to the passing oil.

After the oil enters the inner valve cylinder or sleeve 46 through the'openings II or 12, it proceeds out of the valve cylinder 46 into a chamber or compartment 95, and thence into the cylindrical spring controlled valve 61 through an opening 66 in the end wall 91 of the valve cylinder 61. The valve cylinder 61 is provided with an external annular flange 68 which serves as a stop element to control the limit of opening movement of the valve cylinder 51 in response to the biasing which lubrication is supplied to the contacting surface I22 where the rotating shaft I6 engages a section of the valve block. An oil retaining washer I20 is provided along the side orifice HI and the washer is held in place by a threaded lock ring I24 that is threaded onto a portion I26 of the block.

action of its control spring 06. The cylinder 61 may move in the opposite direction to full closed position, as controlled by the position of a stop surface I04 against which the flange 98 may contact when the valve cylinder 51 is forced against the biasing spring 90 by the increased oil'pressure when the oil enters the compartment 95 prior to passing through the opening 96 in the end wall of valve cylinder 51. As shown in the drawings in Fig. 7, a compartment I02 is formed in the valve block to provide space for the valve cylinder 61 when it is actuated in that direction by the increased oil pressure.

As the oil is circulated through the valve 61, the difference betweenthe pressures on the opposite sides of the end wall 91, at the entering orifice 90, due to the square low drop of pressure as fluid flows through the orifice, acts upon the valve 61 against the biasing spring 99. When the velocity through the orifice 96 exceeds a predetermined value, the valve 51 will be moved by such pressure differential to reduce the effective area of the outlet orifice I04. The velocity of the oil through valve 51 will thus be diminished to the permitted value.

The valve cylinder 51 is also provided with a slot I03 that communicates with the opening I04 in the valve block to permit the oil to pass out of the cylinder valve 51 and through the opening I04 into a discharge conduit I05 that leads to a cooling system for the oil. A conduit I06 returns the cooled oil from the cooling system and supplies it through two conduit connections I01 and I08 to the pressure compartments 23 and 24, respectively, through two self-seating, selfclosing pressure valves I09 and H0, respectively. A by-pass conduit connection II2 connects the conduit I05, leading to the cooling system and the conduit I06 from the cooling system, and serves to by-pass a predetermined portion of the circulated oil so that only a desired percentage will be cooled, all of which is predetermined (or may be adjustably controlled), by the relationship between an opening H5 in the conduit I05 and an opening H6 in the by-pass conduit II2.

I have illustrated, in Fig. 6, a passage II! in the valve block, proceeding from the opening I04 leading to the cooling system conduit I05 and proceeding to a passage H8, to serve the contact By means of the various lubricating passages indicated and referred to, all normally frictionally engaging.- surfaces are lubricated.

The action of the spring valve is such that its opening area is proportional to the pressure of the oil flowing through. The pressure P may be evaluated thus,

a PocA, Pong-g, 01' For VQ and since The curve for that relation Po: Vt

may be represented by curve A in Fig. 10. By adding the thin walled orifice of the centering control valve 45 in series with the spring valve 3|, the additional relation between pressure andvolumetrlc velocity may be established as shown by curve B in Fig. 10. The two curves A and B add up to form curve C which shows a direct proportionality between the oil pressure and the volumetric velocity up to point D. Beyond that point D on the curve, the volumetric velocity is maintained limited to that value, as shown by vertical curve E, irrespective of increase in the pressure. Such control is provided by the volume velocity limiting valve 51, which controls the velocity by regulating the size of the orifice between slot I03 and opening I04. The small hump 0-41 at the lower end of curve C is eliminated in the control system by the small by-pass leak at 3I-a in valve 3|, to reduce the developed pressure to the direct-proportionality shown by line F.

Thus, by the combination of valves having proper correlated functional characteristics the system is controlled to establish a proportional relation between the oil pressure and the volumetric velocity of the displaced oil; and to establish a definite maximum volumetric velocity and, therefore, a maximum procession velocity.

Moreover by controlling the area of the series orifice in valve 45, automatic centering of the gyroscope is established by setting up an artificial temporary center, while the external forces acting against the ship, for example, are not equalized, and the gyroscope tends to precess more in one direction than in the other from its actual neutral or central position.

In order to procure such artificial centering,

the inner sleeve valve element 46 is rotated precession is exceeded, for example, whenever the v ,angle of 35 degrees from vertical is exceeded.

If the deflection should be, for example, v4i) degrees or more, the clutches will not rotate the inner sleeve valve element 46 on returning to center but will remain cooked and held in position by the toggles, awaiting the next stroke.

It the precession exceeds the 35 degrees movement to one side of center more frequently than to the other side, the unbalance will be adjusted for in small steps by the clutches until the artificial center is reached, at which the number of times the 35 degree position is reached will be the same for both sides.

The invention is not necessarily limited to a particular kind of valves, or to the details of construction, or to the arrangement shown, since all of those things may be varied without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim as my invention: a

l. The combination with a gyroscope and a mounting support to permit precession movements of hydraulic means including a substantially non-compressible liquid for damping such precession movements, and means for automatically controlling said damping means to establish centering of the gyroscope with respect to the full range or excursion.

2. The combination with a gyroscope and a mounting support to permit precession movements, of hydraulic means including a substantially non-compressible liquid for damping such precession movements to keep the precessional velocities below a fixed maximum, and means responsive to the angle of precession for controlling the damping function 01' the hydraulic means.

3. The combination with a gyroscope and a mounting support to permit precession movements, of hydraulic means including a substantially non-compressible liquid for damping such precession movements, and means responsive to unbalanced angles of precession for establishing crroespndingly asymmetric damping.

4. The combination with a gyroscope and a mounting support to permit precession movements, or means for damping such precession movements, and means responsive to a progressive average of precession excursions for controlling the symmetry of the damping function.

5.- The combination with a gyroscope rotor, mounted for rotation around a vertical axis, of a gimbal therefor provided with trunnions to permit rotation about a horizontal axis, an extension on one trunnion, and, hydraulic damping means controlled by said extension, said means including an oscillatable vane moved by the trunnion, a housing for the vane and arranged to provide two pressure chambers, a liquid medium in the pressure chambers to resist movement of the vane, and outlet valves connected to the chambers to control the expulsion of the liquid under the pressure developed by the vane.

6. The combination with a gyroscope and a mounting support to permit precession movements, ofhydraulic means including a substantially non-compressible liquid for damping such precession movements, and means for centering the gyroscope with respect to its total excursion, said means including a double entrance valve communicating with the hydraulic means, and unidirectional .clutc'h means for selectively controlling the valve to position the valve centrally with respect to the total excursion of the gyroscope.

7. The combination with a gyroscope and a mounting support to'permlt precession movements, of hydraulic means including a substantially non-compressible liquid for damping such precession movements, including means l responsive to the precession movements in each direction for damping the movements of precession, and means responsive to the respective .precessional excursions for controlling the damping impedance oi the hydraulic means.

8. The combination with a gyroscope and a mounting support to permit precession movements, of hydraulic means for damping such precession movements including a liquid medium. including valve means having two entrance ports, and means responsive to precession movements for forcing the liquid through said ports, and means for unbalancing the areas of said ports in accordance with an unbalance of precession movements.

CLINTON R. HANNA. 

